Snowmobile with a supercharged engine

ABSTRACT

An air charging system for use with a vehicle includes a heat exchanger for cooling an air charge by melting a mass of snow/ice that is external to and in thermal communication with the heat exchanger.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 10/715,296, filed Nov. 17, 2003, which is a continuation ofU.S. Pat. No. 6,651,765, filed May 2, 2002, now U.S. Pat. No. 6,651,765,both of which are incorporated herein by reference.

BACKGROUND AND SUMMARY

The present invention relates to snowmobiles, and more particularly tosnowmobiles with engines having air chargers such as exhaust-driven(turbo) or mechanical superchargers.

Conventionally, snowmobiles have been made small and light weight, yethave relatively powerful engines in order to appeal to the typicalsnowmobile driver. Because of the small size, the packaging of thecomponents in a snowmobile is critical. However, due to its sportingnature, it is also desirable to have a snowmobile that is powered by anengine that is not only efficient and light weight, but also generatessignificant power for its size. So, traditionally, two cycle engineshave been used to power snowmobiles. These engines have the advantagethat they are powerful, yet relatively light weight and compact. Oneparticular disadvantage to the two cycle engine is its emissions—itgenerally exhausts more hydrocarbons and other pollutants than anequivalent four cycle engine due to cylinder charging inefficiencies andthe combustion of lubricating oil, among other things. Also, the twocycle engine tends to operate at a relatively high noise level. Withconcern for the environment and increasing strict emissions requirementsbeing instituted by governments, it is increasingly desirable to usefour cycle engines with snowmobiles.

But a naturally aspirated four cycle engine generally produces lessspecific output per liter of engine displacement than does a two cycleengine. It is not practical to merely increase the engine size due tothe size and weight limitations present in packaging an engine in asnowmobile. Furthermore, the typical transmission employed in asnowmobile limits the upper end of the RPM range for the engine. Toincrease the output of a particular four cycle engine, then, one maywish to employ an air charging system, such as a turbocharger (exhaustdriven compressor) or a supercharger (mechanically driven compressor).However, a conventional air charger will require the use of a highergrade of gasoline in order to avoid detonation and pre-ignition problems(i.e. engine knock), which can over time significantly reduce the usefullife of an engine. This higher grade of gasoline is not always availableto a snowmobile driver along the various trails that he may travel.

Thus, it is desirable to have a snowmobile that is powered by a fourcycle engine which overcomes the drawbacks of limited engine output,while still remaining relatively small and light weight. In particular,it is desirable to have an air charging system that maximizes the engineoutput while not requiring a premium grade of gasoline.

In its embodiments, the present invention contemplates a snowmobile. Thesnowmobile has a chassis that includes a track tunnel portion having afront end, with the front end of the tunnel portion including anintercooler opening, and a wall located adjacent to the front end of thetrack tunnel and the intercooler opening defining a snow/ice retentionarea. A track is located within the tunnel portion, and an engine havingan air intake assembly, an air charging system and an exhaust assembly,is mounted to the chassis. The snowmobile also has an intercooler systemincluding a heat exchanger being disposed adjacent to the intercooleropening and the wall, with the heat exchanger including a charge airinlet and a charge air outlet, and with the charge air inlet being influid communication with the air charging system and the charge airoutlet being in fluid communication with the air intake assembly; and ascreen covering the intercooler opening.

The present invention further contemplates a method of operating asnowmobile engine having an air charging assembly and an air intakeassembly, the method comprising the steps of: compressing intake air inthe air charging assembly; locating snow/ice on a first heat exchangerby providing a snow/ice retention area adjacent to the heat exchanger,and causing snow/ice to be propelled into the snow/ice retention area;passing an intercooler liquid through the first heat exchanger tothereby transfer heat to the snow/ice; passing the intercooler liquidthrough a second heat exchanger; passing the compressed intake airthrough the second heat exchanger to thereby transfer heat to theintercooler liquid; directing the compressed intake air into the airintake assembly; monitoring operating conditions of the engine; andinjecting the intercooler liquid into the air intake assembly under apredetermined set of the operating conditions.

In its embodiments, the present invention also contemplates a method ofoperating a snowmobile engine having an air charging assembly, an engineair intake assembly, the method comprising the steps of: compressingintake air in the air charging assembly; providing a snow/ice retentionarea adjacent to a heat exchanger; causing snow/ice to be propelled intothe snow/ice retention area; passing ram air through the heat exchangerand the snow/ice; passing the compressed intake air through the heatexchanger to thereby transfer heat to the snow/ice; and directing thecompressed intake air into the air intake assembly.

An advantage of an embodiment of the present invention is that a fourstroke engine may be employed with a snowmobile, producing sufficientengine output, while remaining relatively small and light weight.

Another advantage of an embodiment of the present invention is that thecharged air engine in the snowmobile need not require a premium grade ofgasoline to operate properly.

A further advantage of an embodiment of the present invention is thatthe intercooler heat exchanger, by employing snow/ice to cool the chargeair, is very efficient, allowing it to be relatively small and lightweight. This efficiency also allows for minimum pressure loss in thecharge air as it is being cooled in the heat exchanger, thus allowingfor a relatively smaller size turbine in the air charger assembly whilestill providing sufficient pressure in the engine air intake. Thisallows for easier packaging of the components as well as reduced cost.

An added advantage of an embodiment of the present invention is that theengine cold start capability is improved since the engine will operateat higher compression ratios than would otherwise be possible withregular grade gasoline.

Another advantage of an embodiment of the present invention is thatthere is minimal turbo lag in the system since the total air volume inthe engine system is kept to a minimum.

A further advantage of an embodiment of the present invention is thatthe intercooler system for the air charger is effective even duringoperation of the snowmobile under high engine load, low forward speedconditions, such as when climbing a hill.

An additional advantage of an embodiment of the present invention isthat a portion of the intercooler liquid can be injected into the chargeair, thus removing additional heat from the air charge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a snowmobile in accordance with thepresent invention;

FIG. 2 is a schematic view of the snowmobile, including the engine andair charging system of the present invention; and

FIG. 3 is a view similar to FIG. 2, but illustrating an alternateembodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 illustrate a snowmobile 20, which includes a chassis 22 uponwhich is mounted a hood 24 and a seat 26, with a windshield 25 betweenthem. A pair of front skis 28 (only one shown) are each connected to thechassis 22 via a front suspension 30 and are connected to a steeringassembly 32. An engine 34 is mounted to the chassis under the hood 24. Arear portion of the chassis 22 forms a track tunnel 36, which isgenerally located under the seat 26.

Within the track tunnel 36 is mounted a drive track 38. The drive track38 is a loop of rubber (or other suitable) material and includespaddle-like cleats 40. The drive track 38 is generally supported by apair of rear idler wheels 42, a front lower idler wheel 44 and a frontdrive wheel or sprocket 46. Since the invention does not deal with thedetails of the suspension system for the front skis 28 or the drivetrack 38, where any details of these suspension systems are discussed orshown, any conventional structure may be utilized as may be readilyapparent to those skilled in the art. Preferably, there is a rubberizedsnow flap 47, which is mounted behind the drive track 38 in order toallow more snow/ice to be entrained in the tunnel 36 and moved toward anintercooler opening 48.

The track tunnel 36 includes the intercooler opening 48, at the front ofthe tunnel 36 and facing backwards toward the front of the drive track38. There is preferably a screen 50 covering the opening 48 in order tokeep unwanted debris from entering the opening 48. The chassis 22includes a lower wall portion 52 just forward of the opening 48, forminga snow retention area 54. The size of the opening 48, and the height ofthe wall 52 can be sized, as desired, to trap the appropriate amount ofsnow/ice in the retention area 54. Preferably, the opening should bedesigned to prevent bridging, which can prevent the continuedintroduction of snow/ice to a heat exchanger 56.

Located just forward of the opening 48, and forming a bottom portion ofthe retention area 54 is the tunnel heat exchanger 56—this forms part ofan intercooler system 57. The heat exchanger 56 includes cooling fins,upon which snow/ice held in the retention area 54 falls. The tunnel heatexchanger 56 is mounted to the chassis 22, which are both usually madeof aluminum. The heat exchanger 56 includes an air inlet 58 and an airoutlet 60. The heat exchanger 56 can be, for example, a plate-and-shellor an extruded-tube heat exchanger. The later is preferred, and, since,as will be discussed below, the heat transfer is very efficient, thepassage size of its extruded tubes can be relatively large, thusminimizing the pressure loss in the charge air as it passes through thetubes, from the inlet 58 to the outlet 60. There is a flap 62, locatedon the forward underside of the heat exchanger 56.

The chassis 22 also includes a ram air duct 64 located forward of theheat exchanger 56. It has an opening facing forward and extendsrearwardly to the heat exchanger 56, creating a path for air flow to theheat exchanger 56.

The engine 34 has an air intake manifold 66, which is connected to theoutlet 60 of the tunnel heat exchanger 56, and an exhaust manifold 68,which is connected to a turbine 72 in an air charging assembly 70. Theair charging assembly 70 also includes a compressor 74, which isconnected to the air inlet 58 of the heat exchanger 56. The air chargingassembly 70 illustrates a turbocharger, but as would be clear to oneskilled in the art, a supercharger assembly may be employed instead. Theengine 34 will include some type of engine cooling system (not shown),which may employ, for example, air cooling or liquid cooling—but thissystem does not form part of the present invention, and can beconventional in nature, so it will not be discussed further herein.

In this embodiment, the tunnel heat exchanger 56 acts as the primaryintercooler element for cooling the charge air. One will note that theheat exchanger 56 location is ideal since it is adjacent to the track 38at a very good location for receiving snow/ice, and is also locatedclose to the engine 34, thus minimizing the volume of air in the system.Otherwise, the turbo-lag could increase dramatically.

The operation of the snowmobile 20 will now be described. When theengine 34 is started, the exhaust from the engine 34 will drive the aircharging assembly 70, causing intake air to be compressed and pushingthe charged air through the heat exchanger 56 and into the engine intakemanifold 66. As the snowmobile 20 moves forward, some of the snow/icecaught in the grooves of the track 38 or on the track cleats 40 isinertially separated and thrown off as that particular portion of thetrack 56 engages the front drive wheel 46. This is due to the abruptchange in track direction at that location. The snow/ice is throwntoward the intercooler opening 48 because the opening 48 isintentionally located in the path of this snow/ice. So this snow/ice ispropelled through the opening 48 and comes to rest in the retention area54 on top of the heat exchanger 56.

When referring to snow/ice herein, this generally means water in itssolid state, but it may also include some liquid water or water vapor,as the case may be, since it may be partially melted when initiallyentering the intercooler system, and of course will melt when absorbingheat from the charged air. Thus, the term snow/ice means water mostly inits solid state, but also includes some liquid water and some watervapor.

The heat exchanger 56 is oriented to allow for a fall through (or drainthrough) type of flow. This means that, as the charge air flowingthrough the heat exchanger 56 gives off heat to the snow/ice resting ontop, the snow/ice melts. The liquid water will flow down through theheat exchanger 56, via the normal action of gravity, and continue toabsorb heat until it falls out the bottom the heat exchanger 56 orvaporizes. The ram air duct 64 allows air, indicated generally as 76 inFIG. 2, to flow through the duct 64 and then through the heat exchanger56. This ram air duct 64 is optional, but will help to enhanceevaporative cooling and keep the snow/ice piled on top of the heatexchanger 56 moving. In the alternative, a moving blade (not shown) canbe employed to keep the snow/ice in the retention area 54 moving andbreak it up. The flap 62, which is optional, is. mounted against theheat exchanger 56, and will retain some of the melted snow/ice that hasmelted and dropped through the tunnel heat exchanger. This water willthen boil off as it absorbs additional heat.

Since the heat exchanger 56 is directly mounted to the chassis 22, andboth are preferably made of aluminum, which is a good heat transfermaterial, the chassis 22 will also absorb some of the heat from the heatexchanger core 56, further improving the overall efficiency of thesystem.

When the intake air is compressed, by the air charging system 70, itstemperature increases. But, since hot air contains less energy-providingoxygen by volume than cooler air, it will produce less power. A coolercharge of air is denser and can be mixed with more fuel to increaseengine output. Additionally, cooler charge air reduces the tendency forengine detonation (spontaneous combustion). Thus, an effectiveintercooler can greatly improve the engine output.

The efficiency of the intercooler is obtained due in part to the factthat water, when changing phase from a solid to a liquid or a vapor canabsorb a very large amount of heat—significantly more heat than just airor water at ambient temperature. The high heat transfer rate means thatthe heat exchanger core size can be minimized, while the charge airtemperature is lowered substantially—even below ambient air temperatureunder certain conditions. With the very efficient cooling, the tubesthrough which the charge air flows can be made less restrictive, thusminimizing the pressure drop across the heater core. By minimizing thepressure loss, the charge air density is improved. Further, bysignificantly cooling the charge air, this allows for an increase inintake manifold pressure without serious predetonation (i.e. engineknock) concerns, which allows one to obtain even higher performancelevels from the engine.

In the first embodiment, the tunnel heat exchanger 56 is a chargeair-to-snow/ice heat exchanger, which acts directly as the charge airintercooler. Other intercooler system configurations are possible wherethe tunnel heat exchanger 56 does not directly cool the charge air, aswill be discussed in more detail below in regard to FIG. 3.

FIG. 3 illustrates a second embodiment of the snowmobile 120 of thepresent invention. In this embodiment, elements that are the same as inthe first embodiment will be designated with the same element numbers,but those that have changed or been added will be designated with 100series numbers.

In this embodiment, the charge air is not directly cooled by the tunnelheat exchanger 156. A secondary loop, an intercooler liquid loop 178, isadded to improve the cooling performance of the intercooler system 157under certain operating conditions. This intercooler liquid loop 178includes a liquid container 180, which holds intercooler liquid 182. Theintercooler liquid 182 is preferably an inexpensive, easily obtainablefluid, such as, for example, windshield washer fluid used withautomotive vehicles. Although, if one prefers, other suitable liquidsmay be employed. The container 180 is connected to a pump 184, which, inturn, is in fluid communication with the inlet 158 to the tunnel heatexchanger 156. The outlet 160 to the tunnel heat exchanger 156 is influid communication with an inlet 185 to a charge air-to-liquid heatexchanger 186, which, in turn, is in fluid communication with the liquidcontainer 180.

The pump 184 is also in fluid communication with the charge air outputof the air charging assembly 170, via an injector valve 187. Theintercooler liquid 182 can be injected into the charge air in order tocontrol engine knock under certain engine operating conditions.

The tunnel heat exchanger 156 is again mounted below a snow retentionarea 54 in front of an interfolding opening 48, which is again at thefront of the track tunnel 36 in front of the track 38. But, in thissecond embodiment, the tunnel heat exchanger 156 is a liquid-to-snow/iceheat exchanger, and acts as a secondary intercooler element, with thecharge air-to-liquid heat exchanger 186 being the primary intercoolerelement. Thus, the tunnel heat exchanger 156 employs the snow/ice tocool the liquid 182, which, in turn, is employed to cool the charge air.

The compressor 174 of the air charging assembly 170 is connected to anair inlet of the heat exchanger 186, and an outlet of the heat exchanger186 is connected to the engine intake manifold 166. A wastegate 188couples to the turbine 172 to allow for exhaust bypass of the turbine172 if the pressure of the charge air is too high. The wastegate 188 andthe injector valve 187 are controlled by an engine control unit 190,based upon inputs from an intercooler liquid level sensor 191, a chargeair temperature sensor 192, and a knock sensor 193, in addition to otherconventional inputs to the engine control unit 190.

While the intercooler system 157 of the second embodiment is morecomplicated than that in the first embodiment, it provides advantagesthat allow for further enhancements to performance. Under limited engineoperating conditions, such as for transient operation, when engine knockis more difficult to control, as is indicated by the knock sensor 193detecting engine knock, some of the intercooler liquid 182 can bemetered into the intake manifold 166 in order to control the knock. Ifthe level sensor 191 indicates that the liquid level is not sufficientto meter some into the intake, then the engine control unit 190 canlimit some other engine function in order to prevent knock, instead ofmetering the liquid 182 into the air intake. Further, the thermal massof the intercooler liquid 182 can be used to lower the charge airtemperature under transient operation because the thermal mass canprevent a rapid rise of charge temperature.

While certain embodiments of the present invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

1. An air charging system for use with a snowmobile engine, thesnowmobile engine being mounted for propelling a snowmobile over asnow/ice covered terrain, the system comprising: a first heat exchangerfor cooling an air charge, an efficiency of the first heat exchangerbeing enhanced by the first heat exchanger being disposed on asnowmobile such that the first heat exchanger cools the air charge bymeans of latent heat including at least the heat of fusion required tomelt a mass of snow/ice that is separate from the air charge, and thatis in thermal communication with the first heat exchanger, theefficiency of the first heat exchanger being further enhanced byconduction, the first heat exchanger thermally conductive material beingmounted to a thermally conductive structure of the snowmobile such thatheat is conducted from the first heat exchanger thermally conductivematerial to the snowmobile thermally conductive structure; and a secondheat exchanger operating in cooperation with the first heat exchanger tocool the air charge, the second heat exchanger including a liquidreservoir for holding a volume of liquid, the reservoir being in fluidcommunication with the second heat exchanger for convectively coolingthe air charge in the second heat exchanger.
 2. The air charging systemof claim 1, including the first heat exchanger being in thermalcommunication with a mass of snow/ice communicated to the first heatexchanger by the snowmobile from a snow/ice covered terrain.
 3. The aircharging system of claim 2, including the efficiency of the first heatexchanger being further enhanced by the latent heat of vaporization ofentrained water being in thermal communication with the first heatexchanger and being vaporized thereby.
 4. The air charging system ofclaim 1, including the efficiency of the first heat exchanger beingfurther enhanced by convective heat exchange by means of a volume of ramair being moved over the first heat exchanger.
 5. The air chargingsystem of claim 1, wherein the mass of snow/ice is external to the firstheat exchanger.
 6. The air charging system of claim 1, furthercomprising a knock sensor coupled to the snowmobile engine and aninjector valve for selectively injecting liquid from the liquidreservoir into the air charge based on an output from the knock sensor.7. The air charging system of claim 6, further comprising a liquid levelsensor to determine the amount of liquid in the liquid reservoir. 8-13.(canceled)
 14. An air charging system for use with a snowmobile, thesystem comprising a heat exchanger for cooling an air charge by meltinga mass of snow/ice that is external to and in thermal communication withthe heat exchanger.
 15. The air charging system of claim 14, furtherincluding a second heat exchanger including a liquid reservoir forholding a volume of liquid and operating in cooperation with the heatexchanger to cool the air charge.
 16. The air charging system of claim14, further including a snowmobile thermally conductive structure suchthat heat is conducted from the heat exchanger to the snowmobilethermally conductive structure.
 17. The air charging system of claim 14,wherein the heat exchanger includes: an air charge inlet receiving theair charge to be cooled; an air pathway in fluid communication with theair charge inlet; and a snow/ice receiving surface exterior to the airpathway and air charge inlet, the snow/ice receiving surface providingfor the collection of snow/ice thereon to allow heat transfer from theheat exchanger to the snow/ice.
 18. The air charging system of claim 17,wherein the snow/ice receiving surface defines a wall of a snow/iceretention area.
 19. The air charging system of claim 17, wherein thesnow/ice receiving surface is disposed within a snow/ice retention area.20. The air charging system of claim 19, wherein the snow/ice retentionarea includes a snow/ice inlet positioned to receive snow/ice via atrack tunnel of the snowmobile.